With the knowledge that human macrophages express PILRα [24] and confirmation that human PILRα binds human CD99, we next sought to evaluate the effects of blocking the macrophage PILRα:CD99 Ewing sarcoma binding axis (Figure 5B, left panel) on macrophage activity using TNF-α secretion as a proxy. The gene discussed is CD99; the disease is Ewing sarcoma.